When pipe is made by cold roll forming a suitable flat strip of metal to a tubular shape and welding the seam, the tube form passes through pairs of fin-pass rolls each having a fin roll adapted to be inserted between the adjacent lengthwise edges of the tube form so that the adjacent edges may be gradually forced to move toward each other and may be joined together by suitable welding. The present invention relates to an improvement of such fin-pass rolls.
In general, a fin-pass roll comprises right and left fin side rolls for bending a flat metal strip into a tubular shape and a fin roll which is sandwiched between the fin side rolls and is adapted to be inserted between the adjacent edges of the tube form so as to bear against them. FIGS. 1 and 2 show typical prior art fin-pass rolls, and FIG. 3 there is shown an improved fin-pass roll. In FIG. 1, a fin roll 1 and fin side rolls 2 and 3 are assembled with bolts and nuts as a unitary construction and are keyed to a drive shaft 5 so that the fin roll 1 and the side rolls 2 and 3 may be rotated in unison with the drive shaft 5, whereby a tube form 6 is formed and passed. This fin pass roll is split into three sections 1, 2 and 3 in order to overcome the problems encountered when the fin-pass roll is made as a one-piece. That is, when the fin roll 1 or the fin side roll 2 or 3 is worn out, it may be removed for repair or replacement. However the fin-pass roll of the type shown in FIG. 1 cannot eliminate the problem of rapid wear of the portions 7 of the fin roll 1 and the portions 8 of the fin side rolls 2 and 3 against which the adjacent edges of the tube form 6 are forcibly pressed. That is, due to the irregular propagation of wear at these portions 7 and 8 and to the irregularity in shape of the edges of the tube form 6 the fin-pass roll is subjected to impact forces so that frequent rupture or fracture of these portions 7 and 8 results. Furthermore the adjacent edges of the tube form 6 are forced against the fin-pass roll when the tube form 6 passes so that the deformation of the edges occurs and consequently the edges cannot be made into intimate and smooth contact with each other. As a result the edges cannot be perfectly joined to each other by welding. Moreover since the tube form 6 is forced to slide relative to the fin-pass roll, surface quality is considerably degraded.
The fin pass roll of the type shown in FIG. 2 had been proposed in order to overcome the above problems encountered in the fin pass roll shown in FIG. 1. In order to eliminate the slip between the tube form 6 and the fin roll due to the difference between the feed of the tube form 6 and the peripheral velocity of the fin roll 9, the fin roll 9 is so constructed and arranged as to be able to rotate independently of the fin side rolls 10 and 11. As a result wear of the portions 12 of the fin roll 9 against which are forced the edges of the tube form 6 may be considerably suppressed, but the problem of wear and cracking of the portions 13 of the fin side rolls 10 and 11 against which are forced the edges of the tube form 6 cannot be eliminated so that there still remains the problem of rupture or fracture of these portions 13.
In order to overcome the problems encountered in the fin pass rolls of the types shown in FIGS. 1 and 2, there had been proposed a fin pass roll of the type shown in FIG. 3. The fin-pass roll is split into the fin roll 15 and the fin side rolls 16 and 17 in such a way that the fin roll 15 may have arcuate caliber profile which merge with the arcuate caliber profile of the fin side rolls 16 and 17. As a result the fin side rolls 16 and 17 are spaced apart from the edges of the tube form 6 so that the problem of wear of the fin side rolls 16 and 17 may be overcome. That is, wear occurs only on the fin roll 15 at portions 18 and 19 and the replacement or repair of only the fin roll 15 whose tool cost is relatively inexpensive may suffice. In other words, the replacement of the expensive fin side rolls of the fin pass roll shown in FIG. 1 or 2 may be advantageously eliminated. However, the fin roll 15 is still assembled with the fin side rolls 16 and 17 with bolts and nuts as a unitary construction so that the edges of the tube form 6 are still forced against the fin roll 15 and the slip occurs the tube form 6 and the fin pass roll. As a consequence the problem of wear and cracking of the portions 18 and 19 of the fin roll 15 cannot be overcomed. Thus the prior art fin pass rolls have been all unsuccessful in eliminating the fundamental problem of wear and cracking.